Vaccination to infectious diseases should preferably be finished by infancy. For this purpose, many kinds of vaccines need to be inoculated in a fixed period of time. As a devise for efficient vaccination to various infectious diseases, mixed vaccines in which several vaccines are mixed together have been developed. A mixed vaccine has many merits including: (i) it may provide protection to plural pathogens simultaneously, (ii) it may eliminate troublesomeness of inoculation schedule of plural vaccinations, (iii) it may reduce a cost for vaccinations (technical fee) and burden of time for individuals who receive vaccinations with increase in a vaccination rate being expected, (iv) it may reduce burden of medical staff, and (v) it may reduce burden to environments by diminution of waste materials through reduction of vaccination frequency. Thus, for a mixed vaccine, the more vaccine antigens are contained therein, the better.
However, the number of vaccine antigens to be mixed together for preparing a mixed vaccine is limited. Namely, the larger number of vaccine antigens are mixed, the less an amount of each of the vaccine antigens can be administered. Besides, some kinds of antigens may interfere with each other to thereby lead to reduction of their antibody-inducing capacity, which may result in reduction in antibody titer of a vaccine and make efficient protection against infection difficult.
Concrete mixed vaccines that have been published up till the present include a diphtheria/pertussis/tetanus (DPT) mixed vaccine preparation “VACCINE COMPOSITION” (cf. e.g. Patent reference 1), a mixed vaccine containing papilloma virus (HPV) antigen “Novel Composition” (cf. e.g. Patent reference 2), a polyvalent DTP polio vaccine “MULTIVALENT DTP-POLIO VACCINES” (cf. e.g. Patent reference 3), a method for inducing cellular immune activity of a live vaccine in an inactivated vaccine and a mixed vaccine obtained by said method (cf. e.g. Patent reference 4), and the like. In addition to these, mixed vaccines of numerous combinations have already been published. For a Japanese encephalitis virus vaccine, mixed vaccines with DTP vaccine, hepatitis B vaccine (HepB), hepatitis A vaccine (HepA), and the like have been reported (cf. e.g. Non-patent reference 1). Development of a mixed vaccine with more combinations is desired but there is the problem of reduced effect of a vaccine as described above. In order to solve the problem, development of such an adjuvant that allows for a higher antibody titer with as little amount of an antigen as possible is desired.
In general, an adjuvant, when added to a vaccine antigen, is known to enhance immunogenicity of the vaccine antigen and includes an aluminum gel particle (aluminum salt), an oil adjuvant comprising a mineral oil as a main component, a surfactant-like adjuvant such as saponin purified from white hyacinth bean, and a TH1-inducing adjuvant derived from intracellular toxins (LPS, etc.). For an adjuvant for use in a vaccine for animal, an oil adjuvant may be often used which is locally more reactive than an aluminum adjuvant. For an adjuvant to be used in a vaccine for human, however, safety is required in addition to efficacy.
For an adjuvant to be used in a vaccine for human, an aluminum gel has hitherto been used primarily as its efficacy has been proved but recently newly developed MPL and double-stranded RNA have got to be chosen for use. Already known adjuvant compositions include “Vaccine” consisting of an immunostimulating agent (MPL) and a metal salt (cf. e.g. Patent reference 5), an oil-in-water emulsion “Adjuvant composition” (cf. e.g. Patent reference 6) which comprises oil such as 3D-MPL, squalene, alpha-tocopherol, polyoxyethylene sorbitan monooleate, and the like, a synthetic compound adjuvant “Immunologic adjuvant compound” (cf. e.g. Patent reference 7), “Vaccine preparation” (cf. e.g. Patent reference 8) which utilizes cholera toxin, “Use of virus-like particle as adjuvant” (cf. e.g. Patent reference 9) which utilizes virus-like particle (VLP) formed from a particle-forming polypeptide of a surface antigen of hepatitis virus, and many others.
For Japanese encephalitis virus vaccine, an inactivated vaccine is currently used which is prepared by inoculating Japanese encephalitis virus (JEV) into the brain of mice, purifying the virus from the brain with symptoms of encephalitis, and inactivating the virus with formalin. Inactivated JEV vaccines using African green monkey kidney epithelial (Vero) cells in place of the brain of mice have been developed (cf. e.g. Patent references 10, 11 and 12). However, it was not known that these JEV particles have an adjuvant activity.    Patent reference 1: WO2002/080965    Patent reference 2: Japanese patent publication No: 2004-67696    Patent reference 3: WO98/00167    Patent reference 4: Japanese patent publication No: 2001-253833    Patent reference 5: Japanese patent publication No: 2007-262097    Patent reference 6: Japanese patent publication No: 2007-231029    Patent reference 7: Japanese patent publication No: 2002-535411    Patent reference 8: WO00/23107    Patent reference 9: WO98/08146    Patent reference 10: WO00/20565    Patent reference 11: Japanese patent publication No: 2000-83657    Patent reference 12: Japanese patent publication No: 2004-65118    Non-patent reference 1: RESEARCH DISCLOSURE no. 329, September 1991, HAVANT GB ‘POLYVALENT ANTIGEN VACCINE FOR HUMAN USE’ 32975